#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=1e5+1000;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
struct P{
    LL x,d;
}a[maxn];
int main(void)
{
  ///cin.tie(0);std::ios::sync_with_stdio(false);
  LL n,m;n=read();m=read();
  for(LL i=1;i<=m;i++){
     a[i].x=read();a[i].d=read();
  }
  double sum=0;
  for(LL i=1;i<=m;i++){
     if(a[i].d>=0){
        sum+=1.0*n*a[i].x+1.0*n*(n-1)/2*a[i].d;
     }
     else{
        LL t=(n+2-1)/2;
        sum+=n*a[i].x;
        LL num=0;
        if(n&1) num=1.0*(t-1)*t;
        else if(n%2==0) num=1.0*(t-1)*t+t;
        sum+=1.0*a[i].d*num;
     }
  }
  printf("%.8f\n",1.0*sum/(1.0*n));
return 0;
}
